Study of textured n-type silicon photoanodes: Electron microscopy, auger and electroanalytical characterization of chemically derivatized surfaces

Polished (111), (100) and textured (100) single-crystal, n-Si surfaces have been studied in relation to their use as photoanode materials in a photoelectrochemical device. Textured (100) Si is prepared by chemically etching the polished (100) surface. The textured surface consists of pyramids having (111) sides, necessitating the study of polished (111) Si as a comparison. Electron microscopy and Auger spectroscopy have been employed to characterize textured and polished surfaces functionalized with the electroactive reagents (1,1′-ferrocenediyl)dimethylsilane and (1,1′-ferrocenediyl)dichloosilane. Electrochemical techniques have been used to determine coverage of electroactive material, and the textured surface is found to bind about twice as much material as the polished surfaces. The chargetransfer properties of the surface-confined material on the polished (100) and (111) Si are virtually identical: the position of the photoanodic wave corresponding to uphill ferrocene oxidation is within 30 mV and the ferricenium reduction peak is also at the same potential. The textured (100) Si surface shows a slightly more positive (100 mV) photoanodic and dark cathodic peak. Photoelectrochemical cells based on textured (100) Si vs. polished (100) Si are about 20% better in overall efficiency due to lower reflection losses associated with the textured surface.